//! 祖冲之算法
//!

#[derive(Debug)]
pub struct Zuc {
    lfsr: [u32; 17], // 16个31比特寄存器单元S0 ~ S15。S16用来保存临时的结果，LFSR的运行模式有两种：初始化模式和工作模式。
    f_r: [u32; 3],   // 非线性函数(F)包含的2个32 bit的单元变量R1和R2和一个F的输出W
    br: [u32; 4],    // 比特重组(BR),输入为lfsr单元变量，输出为4个32位的X0，X1，X2，X3
}

impl Zuc {
    /// 完全初始化的一个Zuc
    pub fn initialization(k: [u8; 16], iv: [u8; 16]) -> Self {
        let mut zuc = Self::default();
        zuc.key_load(k, iv);
        for _ in 0..32 {
            zuc.bit_reconstruction();
            zuc.f();
            zuc.lsfr_initial_work(Some(zuc.f_w() >> 1));
        }
        zuc
    }

    /// 加密一个字符串，返回key_stream和密文
    /// let mut zuc = Zue::initialization([0u8;16],[1u8;16]);
    /// let (key_stream, ciphertext) = zuc.cryption("Rust");
    /// let plaintext = zuc.decryption(&key_stream,&ciphertext).expect("some");
    pub fn cryption(&mut self, plaintext: &str) -> (Vec<u32>, String) {
        let mut bytes_all = vec![];

        let plaintext_bytes = plaintext.as_bytes();
        let key_stream_len = plaintext_bytes.len() / 4 + 1;
        let key_stream = self.generate_key_stream(key_stream_len);

        for i in 0..key_stream_len - 1 {
            let value =
                u32::from_be_bytes((&plaintext_bytes[i << 2..(i + 1) << 2]).try_into().unwrap());
            let ciphertext = value ^ key_stream[i];
            let bytes = ciphertext.to_be_bytes();
            bytes_all.extend_from_slice(&bytes);
        }

        // 处理尾部
        if plaintext_bytes.len() % 4 != 0 {
            let pad_count = (4 - plaintext_bytes.len() % 4) as u8;
            let mut last_4_bytes = [pad_count; 4];
            let tail = &plaintext_bytes[(key_stream_len - 1) << 2..];
            unsafe {
                core::ptr::copy(&raw const tail[0], &raw mut last_4_bytes[0], tail.len());
            }
            let value = u32::from_be_bytes(last_4_bytes);
            let ciphertext = value ^ key_stream[key_stream_len - 1];
            let bytes = ciphertext.to_be_bytes();
            bytes_all.extend_from_slice(&bytes);
        } else {
            let value = 0x04040404u32;
            let ciphertext = value ^ key_stream[key_stream_len - 1];
            let bytes = ciphertext.to_be_bytes();
            bytes_all.extend_from_slice(&bytes);
        }

        (key_stream, base64::encode(bytes_all))
    }

    // 解密一个字符串
    pub fn decryption(key_stream: &[u32], ciphertext: &str) -> anyhow::Result<String> {
        let mut ret = Vec::new();
        let bytes = base64::decode(ciphertext)?;
        let k_len = key_stream.len();
        if bytes.len() / 4 != k_len {
            return Err(anyhow::anyhow!("密文和key_stream不匹配"));
        }

        for i in 0..k_len {
            let slice_4 = &bytes[(i << 2)..((i + 1) << 2)];
            let value = u32::from_be_bytes(slice_4.try_into().unwrap());
            let value = value ^ key_stream[i];
            let big_bytes = value.to_be_bytes();
            if i == k_len - 1 {
                // 最后一个block
                if big_bytes[3] == 4 {
                    continue;
                }
                ret.extend_from_slice(&big_bytes[0..(4 - big_bytes[3]) as usize]);
            } else {
                ret.extend_from_slice(&big_bytes);
            }
        }
        Ok(String::from_utf8(ret)?)
    }

    /// 生成密钥流
    pub fn generate_key_stream(&mut self, key_stream_len: usize) -> Vec<u32> {
        self.bit_reconstruction();
        self.f();
        self.lsfr_initial_work(None);
        let mut ret = Vec::<u32>::with_capacity(key_stream_len);
        for _ in 0..key_stream_len {
            self.bit_reconstruction();
            self.f();
            ret.push(self.f_w() ^ self.br[3]);
            self.lsfr_initial_work(None);
        }
        ret
    }

    /// 密钥装入
    #[inline(always)]
    pub fn key_load(&mut self, k: [u8; 16], iv: [u8; 16]) {
        for i in 0..16 {
            self.lfsr[i] = ((k[i] as u32) << 23) | (D[i] << 8) | (iv[i] as u32);
        }
    }

    /// LFSR初始模式
    /// u: 31 bits的输入此时为初始模式, None:工作模式
    pub fn lsfr_initial_work(&mut self, u: Option<u32>) {
        // 开始使用的是移位操作，但是结果总是不正确，为了保证正确，使用提升类型运算，也保证了数据不溢出。
        let v = ((2u32.pow(15) as u64 * self.lfsr[15] as u64)
            + (2u32.pow(17) as u64 * self.lfsr[13] as u64)
            + (2u32.pow(21) as u64 * self.lfsr[10] as u64)
            + (2u32.pow(20) as u64 * self.lfsr[4] as u64)
            + ((1 + 2u32.pow(8)) as u64 * self.lfsr[0] as u64))
            % (2u32.pow(31) - 1) as u64;
        if let Some(u) = u {
            // 初始模式
            //self.lfsr[16] = Self::add_mod(v, u)
            self.lfsr[16] = ((v + u as u64) % (2u32.pow(31) - 1) as u64) as u32;
        } else {
            // 工作模式
            self.lfsr[16] = v as u32;
        };

        if self.lfsr[16] == 0 {
            self.lfsr[16] = 0x7fffffff;
        }

        for i in 0..16 {
            self.lfsr[i] = self.lfsr[i + 1];
        }
    }

    /// BR比特重组
    #[inline(always)]
    pub fn bit_reconstruction(&mut self) {
        self.br[0] = (self.lfsr[15] & 0x7fff8000) << 1 | self.lfsr[14] & 0xffff;
        self.br[1] = self.lfsr[11] << 16 | self.lfsr[9] >> 15;
        self.br[2] = self.lfsr[7] << 16 | self.lfsr[5] >> 15;
        self.br[3] = self.lfsr[2] << 16 | self.lfsr[0] >> 15;
    }

    /// 非线性函数F
    pub fn f(&mut self) {
        // W= X0 ^ R1 + R2
        self.f_r[2] = (self.br[0] ^ self.f_r[0]).wrapping_add(self.f_r[1]);

        // R1 + X1
        let w1 = self.f_r[0].wrapping_add(self.br[1]);

        // R2 ^ X2
        let w2 = self.f_r[1] ^ self.br[2];

        // R1 = S(L1(W1L||W2H))
        self.f_r[0] = Self::s(Self::l1(w1 << 16 | w2 >> 16));

        // R2 = S(L2(W2L||W1H))
        self.f_r[1] = Self::s(Self::l2(w2 << 16 | w1 >> 16));
    }

    /// 获取非线性函数F的输出
    #[inline(always)]
    pub fn f_w(&self) -> u32 {
        self.f_r[2]
    }

    /// 复位Zuc
    #[inline(always)]
    pub fn clear(&mut self) {
        unsafe { (self as *mut Self).write_bytes(0, 1) };
    }

    #[inline(always)]
    fn l1(a: u32) -> u32 {
        a ^ a.rotate_left(2) ^ a.rotate_left(10) ^ a.rotate_left(18) ^ a.rotate_left(24)
    }

    #[inline(always)]
    fn l2(a: u32) -> u32 {
        a ^ a.rotate_left(8) ^ a.rotate_left(14) ^ a.rotate_left(22) ^ a.rotate_left(30)
    }

    /// 查表
    fn s(a: u32) -> u32 {
        let mut x = [0u8; 4];
        let mut y = [0u8; 4];
        x[0] = (a >> 24) as u8;
        x[1] = ((a >> 16) & 0xff) as u8;
        x[2] = (a >> 8) as u8;
        x[3] = a as u8;
        for i in 0..4 {
            if i & 0x1 == 0 {
                y[i] = S0[x[i] as usize];
            } else {
                y[i] = S1[x[i] as usize];
            }
        }
        (y[0] as u32) << 24 | (y[1] as u32) << 16 | (y[2] as u32) << 8 | y[3] as u32
    }
}

impl Default for Zuc {
    fn default() -> Self {
        Self {
            lfsr: Default::default(),
            f_r: Default::default(),
            br: Default::default(),
        }
    }
}

// S 盒的定义，查询步骤：
// 把一个2位十六进制数写成二进制，然后对半砍分别4个数字
// 转成十进制作为行、列，然后在对应的S盒的第x行第y列的数字输出
// 比如输入0x99输入LFSR_S0，二进制变成10011001，1001十进制是9，那就取第9行第9列
// 如果是0x12345678，那就0x12进去LFSR_S0，0x34进去LFSR_S1,0x56进去LFSR_S0，0x78进去LFSR_S1，最后结果并在一起
const S0: [u8; 256] = [
    0x3e, 0x72, 0x5b, 0x47, 0xca, 0xe0, 0x00, 0x33, 0x04, 0xd1, 0x54, 0x98, 0x09, 0xb9, 0x6d, 0xcb,
    0x7b, 0x1b, 0xf9, 0x32, 0xaf, 0x9d, 0x6a, 0xa5, 0xb8, 0x2d, 0xfc, 0x1d, 0x08, 0x53, 0x03, 0x90,
    0x4d, 0x4e, 0x84, 0x99, 0xe4, 0xce, 0xd9, 0x91, 0xdd, 0xb6, 0x85, 0x48, 0x8b, 0x29, 0x6e, 0xac,
    0xcd, 0xc1, 0xf8, 0x1e, 0x73, 0x43, 0x69, 0xc6, 0xb5, 0xbd, 0xfd, 0x39, 0x63, 0x20, 0xd4, 0x38,
    0x76, 0x7d, 0xb2, 0xa7, 0xcf, 0xed, 0x57, 0xc5, 0xf3, 0x2c, 0xbb, 0x14, 0x21, 0x06, 0x55, 0x9b,
    0xe3, 0xef, 0x5e, 0x31, 0x4f, 0x7f, 0x5a, 0xa4, 0x0d, 0x82, 0x51, 0x49, 0x5f, 0xba, 0x58, 0x1c,
    0x4a, 0x16, 0xd5, 0x17, 0xa8, 0x92, 0x24, 0x1f, 0x8c, 0xff, 0xd8, 0xae, 0x2e, 0x01, 0xd3, 0xad,
    0x3b, 0x4b, 0xda, 0x46, 0xeb, 0xc9, 0xde, 0x9a, 0x8f, 0x87, 0xd7, 0x3a, 0x80, 0x6f, 0x2f, 0xc8,
    0xb1, 0xb4, 0x37, 0xf7, 0x0a, 0x22, 0x13, 0x28, 0x7c, 0xcc, 0x3c, 0x89, 0xc7, 0xc3, 0x96, 0x56,
    0x07, 0xbf, 0x7e, 0xf0, 0x0b, 0x2b, 0x97, 0x52, 0x35, 0x41, 0x79, 0x61, 0xa6, 0x4c, 0x10, 0xfe,
    0xbc, 0x26, 0x95, 0x88, 0x8a, 0xb0, 0xa3, 0xfb, 0xc0, 0x18, 0x94, 0xf2, 0xe1, 0xe5, 0xe9, 0x5d,
    0xd0, 0xdc, 0x11, 0x66, 0x64, 0x5c, 0xec, 0x59, 0x42, 0x75, 0x12, 0xf5, 0x74, 0x9c, 0xaa, 0x23,
    0x0e, 0x86, 0xab, 0xbe, 0x2a, 0x02, 0xe7, 0x67, 0xe6, 0x44, 0xa2, 0x6c, 0xc2, 0x93, 0x9f, 0xf1,
    0xf6, 0xfa, 0x36, 0xd2, 0x50, 0x68, 0x9e, 0x62, 0x71, 0x15, 0x3d, 0xd6, 0x40, 0xc4, 0xe2, 0x0f,
    0x8e, 0x83, 0x77, 0x6b, 0x25, 0x05, 0x3f, 0x0c, 0x30, 0xea, 0x70, 0xb7, 0xa1, 0xe8, 0xa9, 0x65,
    0x8d, 0x27, 0x1a, 0xdb, 0x81, 0xb3, 0xa0, 0xf4, 0x45, 0x7a, 0x19, 0xdf, 0xee, 0x78, 0x34, 0x60,
];

const S1: [u8; 256] = [
    0x55, 0xc2, 0x63, 0x71, 0x3b, 0xc8, 0x47, 0x86, 0x9f, 0x3c, 0xda, 0x5b, 0x29, 0xaa, 0xfd, 0x77,
    0x8c, 0xc5, 0x94, 0x0c, 0xa6, 0x1a, 0x13, 0x00, 0xe3, 0xa8, 0x16, 0x72, 0x40, 0xf9, 0xf8, 0x42,
    0x44, 0x26, 0x68, 0x96, 0x81, 0xd9, 0x45, 0x3e, 0x10, 0x76, 0xc6, 0xa7, 0x8b, 0x39, 0x43, 0xe1,
    0x3a, 0xb5, 0x56, 0x2a, 0xc0, 0x6d, 0xb3, 0x05, 0x22, 0x66, 0xbf, 0xdc, 0x0b, 0xfa, 0x62, 0x48,
    0xdd, 0x20, 0x11, 0x06, 0x36, 0xc9, 0xc1, 0xcf, 0xf6, 0x27, 0x52, 0xbb, 0x69, 0xf5, 0xd4, 0x87,
    0x7f, 0x84, 0x4c, 0xd2, 0x9c, 0x57, 0xa4, 0xbc, 0x4f, 0x9a, 0xdf, 0xfe, 0xd6, 0x8d, 0x7a, 0xeb,
    0x2b, 0x53, 0xd8, 0x5c, 0xa1, 0x14, 0x17, 0xfb, 0x23, 0xd5, 0x7d, 0x30, 0x67, 0x73, 0x08, 0x09,
    0xee, 0xb7, 0x70, 0x3f, 0x61, 0xb2, 0x19, 0x8e, 0x4e, 0xe5, 0x4b, 0x93, 0x8f, 0x5d, 0xdb, 0xa9,
    0xad, 0xf1, 0xae, 0x2e, 0xcb, 0x0d, 0xfc, 0xf4, 0x2d, 0x46, 0x6e, 0x1d, 0x97, 0xe8, 0xd1, 0xe9,
    0x4d, 0x37, 0xa5, 0x75, 0x5e, 0x83, 0x9e, 0xab, 0x82, 0x9d, 0xb9, 0x1c, 0xe0, 0xcd, 0x49, 0x89,
    0x01, 0xb6, 0xbd, 0x58, 0x24, 0xa2, 0x5f, 0x38, 0x78, 0x99, 0x15, 0x90, 0x50, 0xb8, 0x95, 0xe4,
    0xd0, 0x91, 0xc7, 0xce, 0xed, 0x0f, 0xb4, 0x6f, 0xa0, 0xcc, 0xf0, 0x02, 0x4a, 0x79, 0xc3, 0xde,
    0xa3, 0xef, 0xea, 0x51, 0xe6, 0x6b, 0x18, 0xec, 0x1b, 0x2c, 0x80, 0xf7, 0x74, 0xe7, 0xff, 0x21,
    0x5a, 0x6a, 0x54, 0x1e, 0x41, 0x31, 0x92, 0x35, 0xc4, 0x33, 0x07, 0x0a, 0xba, 0x7e, 0x0e, 0x34,
    0x88, 0xb1, 0x98, 0x7c, 0xf3, 0x3d, 0x60, 0x6c, 0x7b, 0xca, 0xd3, 0x1f, 0x32, 0x65, 0x04, 0x28,
    0x64, 0xbe, 0x85, 0x9b, 0x2f, 0x59, 0x8a, 0xd7, 0xb0, 0x25, 0xac, 0xaf, 0x12, 0x03, 0xe2, 0xf2,
];

/* d的定义，一堆常数，没什么特殊意义 */
const D: [u32; 16] = [
    0x44D7, 0x26BC, 0x626B, 0x135E, 0x5789, 0x35E2, 0x7135, 0x09AF, 0x4D78, 0x2F13, 0x6BC4, 0x1AF1,
    0x5E26, 0x3C4D, 0x789A, 0x47AC,
];
